memcpy

[jackel7777]

pair<char*,char*> tokenize_func(const char* ptr)
{
	size_t len = strlen(ptr);
	pair<char*,char*> alpha_val;
	char *mem = new char[len];
	if(mem == NULL)
	{
			cout<<"error allocating"<<endl;
			exit(0);
	}
	int j=0,i=0;
	
	if(charcmp(ptr,alpha))
	{
		mem[i] = *ptr;
		i++;
		while(charcmp((ptr+i),alpha) || isdigit(*(ptr+i)))
		{
			mem[i] = *(ptr+i);
			i++;
		}
		size_t spare_len =  len -i;
		char *spare  = new char[spare_len];
		if(spare == NULL)
		{
			cout<<"error allocating"<<endl;
			exit(0);
		}
		while(j<spare_len && spare_len > 0)
		{
				spare[j] = *(ptr+i);
				j++;i++;
		}
	
		
			memcpy(alpha_val.first,mem,strlen(mem));
			memcpy(alpha_val.second,spare,strlen(spare));//this causes seg fault

		delete [] mem;
		delete [] spare; 
	}//closes the first if
	
	
	return alpha_val;
}

How do you do a memcopy of the mem and alpha.first without a seg fault.

[Galik]

I think you need to allocate some memory to alpha_val.first and alpha_val.second using new[] before trying to write to them.

[jackel7777]

I agree but however you need to free that memory allocated by alpha_val now which is difficult since you need to return alpha_val. How do you free alpha_val in this case.

[NGen]

Remember that all character arrays containing strings have a null-terminated operator, so the size of the array is actually strlen(str)+1.

[jackel7777]

The srlen(str) + 1 is not the problem . How do we deallocate memory in this case since in the main there is a while loop that will continuously call tokenize and if you dont deallocate the memory, the program might just crash or memory leakage...

[Galik]

The calling function will have to deallocate the pair when its finished with it. Why don't you use string instead of char*?

[jackel7777]

How can calling function deallocate it when alpha_val is local to the fucntion tokenize?

I have not tried with strings before and i might try it. But another option left is to use a class and destroy the object via a destructor.

[Galik]

Although alpha_val is local to the function you return it at the end. So before the local alpha_val is destroyed a copy of it is returned to the caller. You can use delete[] on the pointers stored in the returned copy.

[jackel7777]

k so u r saying i can do a return alpha_val and and then delete alpha_val from the calling function. how can you do that when alpha_val from the perspective of the calling function does not exist as it is local only to tokenize func().

so what i did , i created a class and created an object but allow the object to continously go out of scope...but i find this weird.And now i have a problem as i push the values in a list but since the objects go out of scope, the alpha_val is destroyed via destructor and the list prints some garbage values. How do i copy memory from the heap to another region and add it to the list.

[Galik]

When you put a return var; instruction in your code, you are telling the compiler to make a copy of the variable var. So even though your variable in the function goes out of scope, a new variable is created in the scope of the caller that is a copy of the one that went out of scope.

Try it.